Abrasives for use in oral care compositions such as dentifrices, are required to be effective in removing extrinsic stains, dental plaque and food debris which builds up on the pellicle on the surface of teeth.
In general, the efficiency of physical removal of stain, plaque and food debris can be increased by using an abrasive having increased abrasivity. However, increasing abrasivity also increases the risk that tooth surfaces may be damaged.
Accordingly, there is a continuing need for oral care compositions that demonstrate satisfactory levels of cleaning, yet are not unduly abrasive and damaging to the teeth.
The present inventors have found that this problem can be solved by the use of a calcium carbonate abrasive having a particular particle size and shape.
U.S. Pat. No. 4,743,274 relates to the modification of crystal morphology to provide a high cleaning, low abrading abrasive for use in oral compositions. This describes how, in the case of an abrasive which consists of calcium hydrogenphosphate anhydride (secondary calcium phosphate anhydride), reducing the average crystallite size produces a material which meets both the requirements of high tooth cleanability and low tooth surface abrasiveness.
US2004/0161388 mentions how the dentifrice-relevant properties of a calcium carbonate material are correlated to its morphology and particle size, and describes how small scalenohedral-shaped calcium carbonate particles tend to have relatively insignificant cleaning effectiveness, whereas large rhombohedral-shaped (sometimes referred to as “cubic”) calcium carbonate particles have increased cleaning and abrasive benefits, but often abrade too well: their abrasiveness leading to a concern for possible damage to teeth and gums. As a solution to this problem, US2004/0161388 proposes an abrasive, precipitated calcium carbonate having a primary particle size of about 1 to 4 microns. These primary particles themselves may come together and, through covalent bonding to one another, form aggregates having a particle size of about 3 to 10 microns. The material has a calcite crystalline form and essentially a cubic crystal structure.